Deduction for the actual non-chargeability of 9V batteries.
Because 9V batteries neither an automatic shut-off when reaching maximum charge, nor a discharge function is available, there is here an extreme risk of Übeladung !!
Very unwise (non-) solved !! In my eyes even highly dangerous.
The loading speed of this type of battery is very slow, so that quite expected for standard 9V block battery with charging times of 2-4 days must- so were they empty. Then and only then can / have to calculate the charging time and remove the battery accordingly then.